Field of the Invention
The present disclosure relates to a gas-separation membrane, particularly electrode-supporting type gas-separation membrane module based on ion transport ceramic membrane, its tubular structure and a hydrocarbon reforming method using the same.
Description of the Related Art
Ceramic separation membranes used for gas transport are largely divided into pure oxygen ion conducting membranes and mixed ionic-electronic conducting (MIEC) membranes. The former requires an external power source and electrodes to provide the electric current, and driven by the electrical potential gradient the gas transport is precisely controlled in quantity by applying the electric current supplied and the gas is able to be pumped in either direction regardless of the oxygen partial pressure gradient. In contrast, the latter MIEC membranes are able to transport ionized gas and electrons without electrodes and external power source driven by oxygen pressure gradients. The MIEC membranes consist of one single phase capable of both ionic and electronic conduction or dual phases with one metal (or perovskite) phase for electronic conduction and the other phase from fluorite structures for ionic conduction.
Perovskite comprised in MIEC membranes as described above is chemically unstable because the perovskite structures become destroyed in the presence of acidic or reducing gases such as CO2, H2S, H2O, CH4 etc. by the reaction between the gases and perovskite oxides. Namely, it is hard to use most of the mixed conductive oxides in an actual application process because they are broken down into carbonate or hydroxide in the atmosphere containing CO2, or H2O.
The dual phase MIEC membranes have fluorite oxides which have high chemical stability against acidic or reducing gases as described above. The MIEC membranes were prepared by combining the metal phase selected from Ag, Pd, Au or Pt and the like and the ion conducting phase selected from yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (ScSZ), Sm doped-Ceria (SDC), or Gd doped-ceria (GDC), LaGaO3 and the like. The metal phase and ion conducting phase requires a continuous material pathway leading to a high material cost for preparation. Further it has an issue with the conductivity leading to the lower ionized gas permeation fluxes.
Also among MIEC films, a composite of electro-conductive oxide (for example perovskite type or spinel type) and fluorite structure or fluorite phase having ion conducting properties is essential for preparing a dense composite type separation membrane. However the reaction between the two types of materials during the sintering process results in a lower ionic transport rates. Namely, that is due to the formation of an insulating layer at the interface during the sintering process (Kharton et al., Oxygen transport in Ce0.8Gd0.202d-based composite membranes, Solid State Ionics, 160 (2003), 247).
Therefore, there are needs to develop a separation membrane having a balance between the chemical stability and ionized gas flux. Thus ion conducting ceramic membrane having an external short circuit has been developed, which is consist of a fluorite phase with a dense structure and a porous metal phase that is coated on the surface of the fluorite phase membrane. The two sides of the coated metal layers are connected by external wires and ionized gas conduction through the ceramic separation membrane and electronic conduction (Galvanic method) through the external wire resulted in a short circuit membrane. Silver paste is usually used to seal the ceramic membranes between the two different gas chambers.
The external wires are no longer required if the electronic conduction can be realized via the silver sealing as long as the silver sealing touches the coated porous metal layers. However, the separation membrane with an external short circuit that is based on an ion transport ceramic support has a limitation in preparing them into more thin membranes. Also the scale up of the membrane leads to a longer electronic conduction path and the increased resistance resulting in the lower conductivity. Also this suffers from the high cost of preparing the membrane due to the use of precious metals such as Ag, Pt, and Au for conductive sealing. Thus, there are needs to develop a short circuit membrane which can be scaled up with a reduced thickness and be prepared in a low cost.
KR patent publication 2004-0089964 relates to an oxygen transport separation membrane and discloses an oxygen transport separation membrane and a method for reforming the surface thereof to improve oxygen flux rate, which is composed of mixed conductive perovskite capable of conducting electrons and oxygen ions.
Meanwhile, currently there are no reports regarding tubular modulization of short circuit membranes. Further in configuring a module, the previous art is based on the planar structure and the galvanic method suffers from a high cost for membrane preparation due to the applied voltage required.
U.S. Pat. No. 6,565,632 relates to ion transport membrane assembly incorporation internal support and discloses a tubular membrane. However it suffers from the problem that the area of the membrane per volume is small thus increasing the cost of fabricating the membrane when it is scaled up to fabricate the module having a large capacity. Thus there are needs to develop a module with a compact structure.